Television receiving apparatus



Oct. 7, 1952 E. w. BULL TELEVISION RECEIVING APPARATUS Filed July 24, 1948 5,007 Maan/:771%

Hiv/c5 /mfr Eric Wil icim Bull y/ Patented Oct. 7, `19,52

TELEVISION RECEIVING APiARa'rus Eric William Bull, Hounslowi England, -a'ssignor A "to Electric Ya-Musical Industries-LmitedgHayesi England, a company of Great Britain "Applica-fion July 24, 194s, seiiaiNb. 4(1591 e e In. Great VBritain July 31, 1947'1 e This invention relates to television receiving apparatus of the kind in whichthe tel'evisionimage is reconstituted on the screen of a cathode ray tube. In such apparatus `a cathode ray beam is caused to scan successive lines of the screen Which gives rise to somewhat regular line 'strnc-` ture and in order to obtain maximum resolution the viewer 'tends to; occupy such a distance from the screen that the line structure is readilyv visible., `The reason for the existence of the line structureis that as the television signals are `appliedwto modulate the intensity of the scanning beam the size of the spot on the screen during modulation tends to varyl Thev consequent change in the dimension of the spot transversely of the direction of line scan results in the width oflfie` scanned lines notbeing constant throughout theirlength. It is evident that if the size of the spot wereadjusted so that no, lines were visi- 1 ble forbright parts `of the reconstitutediinage they would, nevertheless, be clearly visible in the grey'and black parts of; the image, whereas` if thesize of-y the spot were adjusted so that no line structure resulted in the black parts of th'eimage losslof definition would occur in the grey and White parts of the image.` ,l

NThe object of the present invention is to4 provide an improved television receiving apparatus i with a'view to rendering the line structure less noticeable; i f

*According to one feature ofthe present invent means are provided for varying the dimens'ior of thevcross-s'ectionof the electron beam Wl'iiclr-liesA transversely to the direction of line scan in accordance with the picture signal amplitude sothat said dimension is made substantially independent of variations which would otherwiseresultdue to the picture signal modulation applied to the beam. Preferably. the crosssection of the electron beam is arranged to have a esubstantially elliptical or elongated form with themajorwaxisbf the beamcross-section lying transversely tothe direction of the line scan, such cross-sectional form of* the beam being imparted thereto by a non-uniform magnetic or electrostatic fleld and the strength of this field-is varied in accordance with ,the picture signal amplitude sov that any'change in the 'major dimension of the. beam cross-section which would otherwise result due to the' picture `signal modulation appliedto the beam is counteracted bythe variation in Said field.

A"It will, be' appreciated that, in general. the

width of a line scanned von the screen of a cath-y ode ray tube' will be smallest at the centre of the screenand will increase as the beam'is-'defiected from the centre of the screen. If the wid-thief the line is 'increased-*so that no spacesare left between the scannedlines atthe centreofthe tube the resolution at the extremities `off-the screen may be lacking. i f A further object lof the present invention is to provide improved television receiving apparatus with a View to'overcoming this defect. v

According to another feature ofthe invention there is provided televisionreceiving-apparatus wherein meansfare provided for varying thed-i# mension of the cross-section of the electron beam which lies transversely to the directionof-line scan in such a manner thatV variations`the width of the linesscanned which wouldy otherwise result as the beam is deflected from its; central position are substantially reduced. Inthismanf` ner the dimension of the spot transversely to the direction of' line scan is maintainedsubstantially -constant over the whole area of theH screen;

-Inorder that the said invention may ybe clearly understood and readily carried into effect, it will now be more fully described withreference to theaccompanying drawings, in which-#1- Figure 1v is a diagrammatic view of= television receiving apparatus embodying a cathode ray tube,` 1` I i Figure 2 isan explanatory diagram',

Figure 3 illustrates one form of means ting up'a non-uniform magnetic field,

Figure4 illustratesmeansfor setting upfa non` uniformlelectrostaticel'd, and i f Figure 5 is a vbloei; diagram `of a circuit'for producing a modulating voltage for maintaining a substantially constant `*width of `lineas-the beam is` deflected from its central position; 1 1

As shown in` Figure l, television receiving; ap paratus comprises a cathode ray tube I provided at oneend with av fluorescent screenA 2 on which a picture is produced by scanning the screenlin a series of horizontal lines in'known mannenlby set-4 a cathodeV ray beamvwhichfiis generated-by a.

the electrode to vary the intensity of the beam it is found that the size of the light spot which is produced on the fluorescent screen 2 tends to vary with the modulation voltage with the result that the width of the lines produced on the screen 2 likewise varies. In order to overcome this defectl the dimension of the'tcross-section of the bearn transversely to the" direction'f oi' line scan is varied so as to counteract the change in dimension which results from the modulatingt voltage applied to the electrode5. The crosssists in making the width of the lines scanned by sectional shape of the electronfbe'am-beforeit f' is deilected by the coils 9 and, mI Il is'made of elonvgated shape in cross-section and, pr eferably elliptical as indicated at II in Figure'2'; with its size due to the picture signal modulation; It is the beam more constant throughout the whole area of the screen as the beam is deflected from the centre of the screen. For this purpose means are provided for varying the dimension of the spot which lies transversely to the direction of vlinegscan lasA the beam is deflected-fromyits cen- Eltral' position., For thispurposethfield set up by the coils I2 in Figure 3 or the electrodes I4 lof Figure 4 is varied by applying further modula- ,tion thereto in addition to the modulation which is necessary to'counteract the variation in spot it foundtofa-rst approximation that the further major dimension of cross section lying transversely of the direction of linev scan,.suchtshape' I 1 being imparted to the beam by causing the'beam to pass through a non-uniform electromagnetic'. 1;

eld which is set up prior to the deflecting coils 9m and lll., Such lnon-uniform magnetic field may befDrQQlllQed bya pair ofi coils I2 asindicatedin Figure 3 and the strength of thefiielud set up by thesefcoilsiis varied in accordance with the pic-y turesignalamplitude in such a manner thai-any variation inthe dimension ofthe electron beam whichl lies transversely of lines scannedproduced as a result of the signal voltagefapplied to the modulating electrode 5 is `c ounteracted by the variation in-.the iield produced by thecoils I2.

orderV to :vary ,the strength of vthe field `produced by ,tl1 e, 4coils I2, the-.currenpvfrpm a source I iisg-,Spiteblyfveried in accordance.; .with thepiei'.ure,ysignal,amplitude,f Ifgthe television yreceiver isopeijating to receive signals in which reduction carrier, k amplitude y is representative -.of .I AMiri,- creasingblackness in the picture,` thegcurrent frornthe source I3 4will berequiredto be varied inversely with respectto the picture signalsqbut modulation required is approximately proportional to thesquare of the distance of the spot from,` 'l 'theicentreof the screen. Consequently, the re- "quired modulation can conveniently be obtained by ,integrating with the output of the line and frame scan generators adding the integrated outputs and then employing these added 4componentslto. effect the required modulation". 'The block diagram shown in Figurev is representar tive of..a circuit suitable for deriving" almodue latine signalfor'mthe ,abovepurpose erence numeral I6 indicatesfthe line scanfgenji two generators produce inf their outputs sawtoothfvoltages a: andy at line and-framef f, quencies respectively which are fed to "integrati ingfcircuits I8 rand ISJ'respectively which inftlieiv 1 outputs' generate respectively voltages equal to 2 ja ndy2, these 4two voltages being thenaddd l in anadding circuit 42l) the added output :t2-14111 is set up t0 produee. the. ellepef'" thebeemlown inFigure 2.- In this embodiment of the invention'sa pair of arcuate ,shapedelectrodes Mare provided, 2through which the ,bean-rv passesprior to dee'ction'by-thecoils -il and I 9,5, ofelectrodes III` are-fed `in pushpuslfi; with suitablevoltages fromvasourcel which .varyinsacf cordance with thegpictulewgnal,amplitude, so thatany tendencyier .the dimensie?1 ef .thespet which: lies transversely; to the a direction .offline scanf to varyfwithgthefpicture,signals ispo teracted..tuik x: J: l; Ttwillj-begappreciated that iin general thezwidth ofaline ls cannedfor-i lthe screen 2,foi;the tube I will be. .smauest atthe @entre erettile; S-teep,arid will-:increase as ithejbeam, is deflected frorn the centre of the screeni This is Vdue .to the fact that in generalthe. curvature of theend of thejtubejl enwhich the screen-2. isdepesitee @Gespot form tothe curvatureofhafsph ,centeredat the: point :about which the, beam l: li Another feature ot the lpresent A"vnventi-o'n coni-I d the-pair.

deflected.

being then applied to a Vmodulator-2l t'o' which the' picture signals'are also fedfthe modulated output being vthen applied in a suitable-manner to the coils I2 of Figurevv 3 or the 'electrodes-f I4 of Figure 4 'with' the result that I not .only is i any tendency for the dimension'of thes'pot'whio'h lies transversely to the direction of vlinefscantjo vary-with the picture' signals counteracted but `also any variation inlthewidth of theillinesffs th 'beam' is deflecte'd from :its centralposition is also reduced. This.; feature ofthe-invention can of course be employed- 'independentlyf-,ofjllil means for counteracting :the I tendencyl for g Vthe saidfdim'ensio'nof thespottotvary withgthe pic;

ture csignals. Asstatedyabove, the modulatingn; lnof z potential which is derived from the circuitsho in Figure 5 correctsthe variation. in the the linesiscanned' asy the; beam is. deecte to a rst approximationgvwhch-iszprobabl i cient': for, practical purposes. .Howeyer it ther correction is requiredhighertermsin and ywill be. required whichcan be deriv e'd, fromz'V circuits described in the United` States,applicA tion Ser. Noi6,053,,file dg,;Febriiary3, l9 EricwLawrence Casling Whitefo Th rmioni" 2,512,016i'f11ed August-, legitimiert@ Willie Eibourn. for T hermlene; Valve ,Cireetes and United StatesgPatent No. 2,572,792,1iled'A Thermionic Valve Circuitsl .-1.:What '1. clepimie'a j i.

,',lelerielen erllkereeetre 'eppe'riet prising fa cathode vifjayf-tube having a' 'screeiltfvf reconstituting `an' imag-ie,` vmeans Afor Vvaryifri'g' t intensityiofthe,beampf saidtube under'th: l'

trol of Ipiety rejsig spot reproduced on said'screen't'e'n to meansI forcausing said v beam `to scan The rer-q erator cfa television'frece'iv'er and the,re ference i numeral II'the frani'efscan" generator.v These an elongated form in cross section with the major dimension of cross section lying transversely of said lines, means for varying said major dimension, means for generating control signals varying in accordance with the amplitude of the picture signals, and means for applying said control signals to change said dimension in accordance with said signals to counteract the tendencyy 5. Television receiving or like apparatus com prising a cathode ray tube having a screen for reconstituting an image, means for generating `line and 'frame frequency oscillations for de- `fleeting the beam of said tube over said screen at line and frame frequencies, means for imfor the spot size to vary` and to maintain the l ing the strength of said eld.

3. Television receiving or like apparatus comprising a cathode ray tube having a screen for reconstituting an image, means for deiiecting the `beam of said tubeI in a series of lines over said screen, means for imparting to said beam an elongated form in cross section with the major dimension of cross section lying transversely of said lines, means for varying said major dimansion, means for generating control signals Varying in accordance with the distance of said beam from the centre of said screen, and means `for applying signals to said dimension varying means to vary said dimension to cause the width of said lines to be maintained substantially constant as said beam is deflected from the centre of said screen.

4. Apparatus according tofclaim 3, wherein said means for imparting saidelongated form comprises a non-uniform field, and said means for varying said dimension comprises means for varying the strength of said field.

`parting to said beam an elongated form in cross section with the major dimension of cross section lying transversely of the direction of line scan, means for Varying said major dimension, means for integrating the line frequency oscillations, means for integrating the frame frequency oscillations, means for 4adding said integrated oscillations, and means for applying-said added oscillations to said means for varying said dimension to maintain the width of the lines scanned substantially constant as said beam is deflected from the centre of saidv screen.

ERICv WILLIAM BULL.

REFERENCES CITED The following references are of record in the le of this patent:

l UNITED STATES PATENTS 

